1. Field of the Invention
This invention relates to a wiper motor for driving a wiper apparatus in order to wiper rain drops, dust and the like adhering to the windshield of, for example, a motor vehicle, and especially to an improved wiper motor suitable to drive a wiper apparatus which is so designed as to reverse the rotational direction of the wiper motor in response to a changeover in the rotational speed of the wiper motor, and decrease length of a motor arm of the wiper linkage at the time of high speed rotation as compared with the length at the time of low speed rotation of the wiper motor through an arm length adjusting device including an eccentric mechanism attached to the motor arm of the wiper linkage in order to solve a difference in the wiping range by the wiper blade between the time of high speed operation and low speed operation of the wiper blade caused by a difference in the inertial force of the wiper blade.
2. Description of the Prior Art
As a device for wiping rain drops adhering to the windshield of the motor vehicle or so, and ensuring the wide visual range of the driver, wiper apparatuses with various structure and function have been used. Recently, a wiper apparatus which is designed so as to be possible to switch over the operation speed of the wiper blade to continuous actuation in high and low two-level or intermittent actuation at a low speed according to the amount of rain-fall is used generally.
In the wiper apparatus of this kind, kinetic energy of the wiper blade at the time of high speed operation becomes larger than that of the wiper blade at the time of low speed operation, therefore a phenomenon is observed in that the wiping range of the wiper blade at the time of high speed operation becomes wider as compared with the wipeing range at the time of low speed operation of the wiper blade according to the difference in the inertial force of the wiper blade. Accordingly, there is defectiveness in that the windshield partially remains unwiped and the visual field becomes narrow at the time of low speed operation in a case where the wiping range of the windshield is set on basis of the oscillation range of the wiper blade at the time of high speed operation, and the moulding of the windshield flame interferes with the wiper blade at the time of high speed operation in a case where the wiping, range of the windshield is set on basis of the oscillation range of the wiper blade at the time of low speed operation.
Applicant proposed previously a wiper linkage which was so designed as to solve the difference in the actual wiping range enlarged owing to the inertial force of the wiper blade by setting the rotational direction of the wiper motor reversely at the time of high speed operation against the rotational direction at the time of low speed operation, making the substantial length of the motor arm of the wiper linkage at the time of high speed operation shorter than that of the motor arm at the time of low speed operation through an arm length adjusting mechanism attached to the motor arm and used with an eccentric bush to be turned as much as 180xc2x0 at the time of switching the rotational direction of the motor arm and reducing the structural wiping range of the wiper blade at the time of high speed operation as compared with that of the wiper blade at the time of low speed operation in Japanese Patent Application No. 10-158026/98 in order to solve the difference in the wiping range caused by the difference in the operation speed of the wiper blade in such the conventional wiper apparatus.
In the newly proposed wiper linkage as mentioned above, it is different from the conventional wiper linkage fundamentally in the point that the rotational directions of the wiper motor in the high-speed mode and the low-speed mode are different from each other, therefore it becomes necessary to control the wiper motor in a manner different from the conventional wiper apparatus in changeover control of the mode, auto-stop control at the time of stopping the wiper device and so.
In such the control, although it is necessary to perform the control by referring to the present position of the wiper blade, that is a position signal generated from a position switch disposed in the wiper motor, there is a problem in that it is not always possible to obtain a position signal suitable to control the aforementioned wiper linkage by the construction of the position switch provided in the conventional wiper motor. Accordingly, development of the wiper motor provided with a position switch having conductive plates arranged suitably to generate the position signal for controlling the aforementioned wiper linkage has become an subject in the wiper device including the wiper linkage which is designed so as to solve the difference in the wiping range caused by the difference in the operation speed of the wiper blade by making the rotational direction of the wiper motor at the high speed operation different from that at the low speed operation.
This invention is made in view of the aforementioned problem in the conventional wiper motor for driving the aforementioned wiper linkage in which rotational directions of the wiper motor are different between the high-speed mode and the low-speed mode, and it is an object to provide a wiper motor provided with a position switch which generates a position signal changing in response to arrival of the wiper blade at the lower turning position and the upper turning position, is possible to automatically stop the wiper blade at the home position (lower turning position) in accordance with an off-operation of the wiper switch, and possible to change the rotational direction together with the rotational speed smoothly and speedily in response to a changeover operation of the wiper mode thereby enabling the control to solve a strange impression raised along with the reversal of the wiper motor.
In order to accomplish the aforementioned object, the wiper motor according to this invention is especially provided with position-detecting conductive plates as a position switch which are composed of a semi-ringshaped high-potential conductive plate connected to a power source, a semi-ringshaped low-potential plate grounded and disposed oppositely to the high-potential plate, and a common plate disposed in a center part between the high and low-potential plates and electrically connected to a movable contact to rotate in a state of being in contact with the high or low-potential plate according to movement of the wiper blade. The signal change is detected in the position signal from the common plate at the time when the wiper blade arrives in the lower turning position and the upper turning position or positions just before these turning positions by setting, for example, two openings existing between the high-potential plate and the low-potential plate in correspondence to the lower turning position and the upper turning position of the wiper blade, respectively. Accordingly, by stopping or reversing the rotation of the wiper motor in response to the signal change in the position signal generated from the common plate (position switch), the wiper blade stops automatically and accurately at the lower turning position (home position), and the rotational direction and speed of the wiper motor are change over at the time of arrival at the lower turning position or the upper tuning position of the wiper blade, whereby the wiper mode is changed speedily in response to the wiper switch operation as compared with a case the wiper mode is changed only when the wiper blade is in the lower turning position. Furthermore, it is solved improper behavior such that the wiper blade changes the direction at halfway in the wiping range of the wind shield.
In the wiper motor according to a preferred embodiment of this invention of which common plate is provided with a connecting plate portion extended through one of two openings formed between the high and low-potential plates, the three conductive plates forming the position switch, the high-potential plate, the low-potential plate and the common plate are disposed on the same plane, therefore the position switch is simplified in construction. In the wiper motor according to another preferred embodiment of this invention, a first opening of the aforementioned two openings corresponds to the lower turning position of the wiper blade, a second opening of the two openings corresponds to the upper turning position of the wiper blade and the connecting plate portion of the common plate is extended through the second opening, therefore the wiper blade stops at the lower turning position automatically and more accurately by making the first opening narrower than the second opening.